1. Field of the Invention
This invention is directed to a new flexible high damping, damage tolerant propeller.
2. Brief Description of the Prior Art
Some retractable pitch propellers are currently made using metallic materials. Their basic purpose is to improve the hydrodynamic performance of a boat. When the boat is not under power, the propeller folds up and causes less drag. The structural material used in all cases are metals which have limited strain capability and are permanently deformed when impacted causing degradation to hydrodynamic and acoustic performance.
U.S. Pat. No. 4,097,193 illustrates an elastomeric damping arrangement for damping vibrations of a structural member, such as a vibration prone airfoil, particularly a helicopter rotor blade tending to vibrate under dynamic deformations. The damping materials illustrated are silicones, various rubber compounds or polyurethane with polyurethane being preferred because of its good bonding and processing capabilities.
According to U.S. Pat. No. 4,797,066 the propeller blade at an increased service load automatically optimizes its pitch, thus reducing or preventing cavitation wherein flexibility is obtained for the propeller utilizing plastic materials having anisotropic properties, i.e. from materials with different physical characteristics in different directions. The propeller's improved properties are achieved by having the reinforcement (the armoring) applied in sections, with the reinforcing elements in one section extending in the same direction, but with the reinforcing elements of one section extending in a direction other than the corresponding elements of another section.